In larger installations, such as Groucho Marx University,
Ethernet is usually not the only type of equipment used.
At Groucho Marx University, each department's LAN is linked
to the campus backbone, which is a fiber optics cable running
FDDI (Fiber Distributed Data Interface). FDDI uses an
entirely different approach to transmitting data, which basically
involves sending around a number of tokens, with a station only
being allowed to send a frame if it captures a token. The main advantage
of FDDI is a speed of up to 100-Mbps, and a maximum cable length of
up to 200-km.

For long-distance network links, a different type of equipment is
frequently used, which is based on a standard named X.25. Many so-called
Public Data Networks, like Tymnet in the U.S., or Datex-P in Germany,
offer this service. X.25 requires special hardware, namely a Packet
Assembler/Disassembler or PAD. X.25 defines a set of networking
protocols of its own right, but is nevertheless frequently used to
connect networks running TCP/IP and other protocols. Since IP packets
cannot simply be mapped onto X.25 (and vice versa), they are simply
encapsulated in X.25 packets and sent over the network.

Frequently, radio amateurs use their equipment to network their
computers; this is called packet radio or ham radio. The
protocol used by ham radios is called AX.25, which was derived from
X.25.

Other techniques involve using slow but cheap serial lines for
dial-up access. These require yet another protocol for transmission
of packets, such as SLIP or PPP, which will be described below.